Spinal cord stimulation is a well accepted clinical method for reducing pain in certain populations of patients. A Spinal Cord Stimulation (SCS) system typically includes an Implantable Pulse Generator (IPG), electrodes, at least one electrode lead, and, optionally, at least one electrode lead extension. The electrodes, which reside on a distal end of the electrode lead, are typically implanted along the dura of the spinal cord, and the IPG generates electrical pulses that are delivered through the electrodes to the nerve fibers within the spinal column. Individual electrode contacts (the “electrodes”) are arranged in a desired pattern and spacing in order to create an electrode array. Individual wires within one or more electrode leads connect with each electrode in the array. The electrode lead(s) exit the spinal column and generally attach to one or more electrode lead extensions. The electrode lead extensions, in turn, are typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG is implanted. Alternatively, the electrode lead may directly connect with the IPG.
SCS and other stimulation systems are known in the art. For example, an implantable electronic stimulator is disclosed in U.S. Pat. No. 3,646,940, issued Mar. 7, 1972, entitled “Implantable Electronic Stimulator Electrode and Method,” teaches timed sequenced electrical pulses to a plurality of electrodes. Another example, U.S. Pat. No. 3,724,467, issued Apr. 3, 1973, entitled “Electrode Implant for the Neuro-Stimulation of the Spinal Cord,” teaches an electrode implant for neuro-stimulation of the spinal cord. A relatively thin and flexible strip of biocompatible material is provided as a carrier on which a plurality of electrodes reside. The electrodes are connected by a conductor, e.g., a lead body, to an RF receiver, which is also implanted and is controlled by an external controller.
In U.S. Pat. No. 3,822,708, issued Sep. 9, 1974, entitled “Electrical Spinal Cord Stimulating Device and Method for Management of Pain,” teaches an SCS device with five aligned electrodes which are positioned longitudinally along the spinal cord. Current pulses applied to the electrodes block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes have a repetition rate of 5 to 200 pulses per second. A patient-operated switch allows the patient to change the electrodes that are activated (i.e., which electrodes receive the stimulation pulses from the IPG) in order to stimulate a specific area of the spinal cord, as required, to better block the pain.
An SCS system treats chronic pain by providing electrical stimulation pulses through the electrodes of an electrode array to the nerve fibers of the spinal cord. The electrode array is situated within the epidural space of the spinal cord. A clinician defines the characteristics of the stimulation pulses by adjusting various stimulation parameters, thereby changing the location and manner of stimulation to the tissue of the spinal cord. A clinician may determine an effective stimulation parameter configuration based on the feedback of the patient to various stimulation configurations. This process of adjusting stimulation parameters to determine the most effective configuration of a parameter set is known as an SCS system fitting procedure.
Two of the most important issues encountered during an SCS system fitting procedure are comfort and power consumption. Comfort is essential to a patient, for this is the purpose of the SCS system implantation: to relief pain. During the fitting session, multiple stimulation parameter configurations may be identified which demonstrate similar comfort levels, or paresthesia benefits, for the patient. However, each of these configurations of similar comfort likely consumer power at very different rates.
Selecting a configuration with minimal power consumption is essential to prolonging the effective life of a battery-powered IPG in an SCS system. If a configuration depletes the battery power of the IPG too quickly, the IPG will require more frequent and longer battery recharging sessions. The more frequent and longer the battery recharging sessions, the sooner the patient will be required to endure another intrusive operation to remove the IPG and replace it with a new IPG.
As mentioned earlier, configurations that seem to provide equal paresthesia to a patient may consume power at very different rates. Yet, for each of these given parameter configurations, there is no immediate information given to the clinician regarding the power consumption for each configuration. Thus, it is difficult for the clinician to compare the power consumption efficacy of one parameter configuration to another. There is also no method for using the power consumption measurements of configurations that have been evaluated to guide the clinician to a lower power consumption configuration with equal paresthesia benefits.
What is needed is an indication of the power consumption for each stimulation parameter configuration being evaluated, and a method for using the power consumption information to help locate a low power consumption configuration.